It is important during neurosurgical procedures to identify and preserve eloquent functional cortex adjacent to a resectable lesion. Intraoperative real-time functional mapping techniques now available cannot be used in many surgical situations and are not sufficiently reliable in all cases in which they are used. We have developed an intraoperative approach that may permit lesion localization and brain functional mapping in real time with minimal risk. This approach makes use of infrared (IR) technology to identify functionally active eloquent cortex and to differentiate abnormal tissue from normal cortex. The method is based on an analysis of the spatial and temporal dynamics of cortical temperature changes obtained by recording the intrinsic cortical IR radiation (3-12 micro/m wavelength band). The goal of this study is to investigate the clinical use of intraoperative IR neuroimaging to differentiate intracranial lesions from surrounding normal functionally important tissue in real time. Reliable real-time intraoperative functional mapping of eloquent cortex adjacent to lesions by this technique would improve the safety and effectiveness of many neurosurgical procedures.